BossCEff / Boss Cap Efficiency
Within the Joint Research Project "Boss Cap Efficiency - BossCEff" funded by the German Ministry of Economy and Technology (BMWi) the Institute for Fluiddynamic and Ship Theory - FDS at the Hamburg University of Technology - TUHH works on the Project "Boss Optimisation - BossOpt".
The existence of a hub vortex has in different ways a negative influence on the performance of a marine propulsors.
First negative effect is the formation of hub vortex cavitation. Normally the rudder is positioned in a line with the propeller shaft which ends with the hub cap. In the hub vortex core the pressure falls below the vapour pressure so cavitation bubbles arise. In that case the cavitation hits the leading edge of the rudder. As cavitation effects erosion the described process should be avoided.
Second problematic effect is the influence of the hub vortex on the propulsion performance. The low pressure region in the core of the hub vortex causes a force on the propeller hub. This force works against the thrust force and therefore also reduces the propeller efficiency. For this reason the appearance as well as the existence of hub vortices itself should be investigated in this project.
With the project "BossCEff" it is intended to increase the efficiency of marine propulsors by reducing the intensity of the hub vortex. In order to achieve that an automated design method will be developed. This design method allows to optimise the hub cap for a given propeller geometry.
In order to realise an automated optimisation tool to design propeller hub cap geometries, different single topics have to be dealt with.
The hub vortex is relevant influenced by viscous effects. For this reason calculation methods for viscous flow have to be used. As the calculation time for a propeller simulation with such a method is much to long, a coupled method is used. Here a coupling between calculation methods for a viscous flow (ANSYS CFX) and for potential theory flow (panMARE) is used.
Next the capability of panMARE to simulate hub vortices and its effects has to be analysed. For this purpose further numerical investigations on idealised geometries are executed as well as model tests are arranged.
An automated improvement of propeller hub geometries can only be enabled by optimisation algorithms. Therefore such a algorithm has also to be integrated in the optimisation process. Here an evolutionary algorithm will be used.
The last step is to bring all single previously presented parts together to one coupled optimisation process.
The work is sponsored by the German Ministry of Economy and Technology (BMWi) under the aegis of the project BossOpt.